The invention relates to a fluid-tight protective system for an electromechanical component, for example a relay, in which an insulating covering is disposed over casing joints or apertures to be sealed, and to methods of sealing such a component.
Where electrical components are used on circuit boards, modern soldering techniques require that not only the circuit boards themselves but also the individual components are at least partially immersed in soldering and cleaning baths. This involves the risk of liquid and gaseous substances penetrating through holes and apertures into the inside of a component and there contaminating contact surfaces, for example. Components such as relays, for example, which for the most part admittedly have a dust cap but are not fitted with a hermetically sealed casing, would become much more expensive if they had to be made with a hermetically sealed casing just for the soldering process although such a casing would be unnecessary for subsequent operations. Consequently, many attempts have been made to make such components fluid-tight for soldering on circuit boards using simple and inexpensive protective devices and thereby provide at the same time a certain amount of protection against the damaging effects of industrial atmosphere.
In the case of relays, the problem is mainly one of sealing the joints between a base and a protective cap and the apertures provided in the base for the contact connections. Various possibilities have already been suggested such as thermoplastic distortion of the casing parts using ultra sound or a hot die, or again casting the casing in a plastic compound. In many cases these methods provide the desired success but only at considerable expense. Casting components frequently cannot be used because this causes the casting compound itself to flow inside the casing and provoke contamination. In addition, German Published Specification No. 21 29 918 proposed fitting a thermoplastic insulating element in the form of a film or shell over the connecting pins with close-fitting holes. Even this method does not provide adequate sealing in every case as such films frequently are affected by temperature and become distorted and then possibly no longer fit snugly enough around the connecting pins of the component.